In the internet, network-based mobility (see non-patented document 1, for instance) and host-based mobility (see non-patented document 2, for instance) have been known as the technologies that offer IP-layer mobility of a node to permit its continuation of communication with another node at the opposite communication end even if the node changes its connection from one link to another as it moves.
For example, Proxy Mobile IPv6 (PMIPv6, hereinbelow) as the network-based mobility disclosed in non-patented document 1 sets up a PMIP network for the network, to which a mobile node is connected, and in which an access gateway (PMA: Proxy Mobile Agent) as a default router for the mobile node and a position managing apparatus (HA: Home Agent) for managing the PMA to which the mobile node attaches itself are defined.
The HA assumes the PMA to which the mobile node is connected as the positional information of the mobile node and manages the identification information on the mobile node in association with the identification information on the PMA. In the HA, the PMA to which the mobile node is connected is continuously updated as the mobile node moves so as to maintain the positional information.
The mobile node has a unique IP address which identifies itself and transmits a packet to the PMIP network by designating the IP address for the receiver and sender of the packet to be communicated between mobile nodes. The PMA to be the point of connection of the mobile node in the core network forwards the packet to the HA. The HA determines the PMA to which the destination mobile node is attached, based on the positional information and forwards the packet.
Accordingly, inside the PMIP network, a forwarding route is established between the HA and the PMA so that the packet is conveyed between mobile nodes by packet forwarding.
In PMIPv6, the mobile node continues communication by only changing the PMA as a default router as the mobile node moves. Inside the PMIP network, the positional information is updated in the PMAs and HA so as to perform packet forwarding to thereby realize communication between mobile nodes. The mobile node continues communication by changing PMAs as it moves, but it can continue using the unique address if it connects to any PMA. This makes it possible to minimize the movement process to be effected by the mobile node and brings about the advantage that the number of control signals can be reduced in the wireless section.
On the other hand, non-patented document 2 describes Mobility Support in IPv6 (MIPv6 hereinbelow) as one example of host-based mobility. MIPv6 defines a mobile node that changes the point of connection to the network with moving and a position managing apparatus (HA: Home Agent) for performing positional management of the mobile node.
A mobile node holds a unique and unvaried IP address that identifies itself on the network, and uses it as the receiver and sender of a transmitted/received packet in communication between mobile nodes. Further, the mobile node acquires an address on a visited network and the acquired address is registered as its positional information to the HA. In the HA, the IP address that identifies the mobile node and the IP address acquired at the visited site for identifying the position are managed in association with each other.
The packet which the mobile node sends out to another mobile node is forwarded by the HA based on the address acquired at the visited site. Specifically, the packet which mobile node 1 transmits to mobile node 2 is forwarded to the HA by tunneling the IP packet having the address of mobile node 1 acquired at the visited site set as the sender and the HA set as the receiver. The HA solves the positional information of mobile node 2 on the receiver side and forwards the transmission packet to the address of mobile node 2 acquired at the visited site, by tunneling the IP packet having the HA set as the sender and the address of mobile node 2 acquired at the visited site set as the receiver. The packets between mobile nodes are delivered in the above way.
In the internet, it was conventionally impossible for a terminal to continue communication by changing its connection point, but the aforementioned PMIPv6 and MIPv6 have enabled a mobile node to continue communication using a single IP address even if the mobile node changes its network connection point.
In PMIPv6 and MIPv6, a mobile node can move while changing its connection point. However, it is impossible for a mobile node to have a plurality of transmitter-receivers and establish connection to networks at the same time. In order to solve this problem, Multiple Care-of Addresses Registration (MCoA hereinbelow) (see non-patented document 3, for instance) has been defined.
In MCoA, the mobile node includes a plurality of transmitter-receivers, which each register an address obtained from the networks to which they connect, as their positional information, to the HA. A series of registering procedures is expanded based on MIPv6. The difference from MIPv6 is that the mobile node registers plural positional information addresses to the HA and that the HA and the mobile node have a plurality of packet delivery routes. The HA and the mobile node can transmit a packet using a delivery route selected based on the type of the packet or preferences when the packet is delivered.    Non-patented document 1: S. Gundavelli, et al., “Proxy Mobile IPv6”, draft-sgundave-mip6-proxymip6-01, January 2007;    Non-patented document 2: D. Johnson, et al., “Mobility Support in IPv6”, RFC 3775, June 2004; and    Non-patented document 3: R. Wakikawa, et al., “Multiple Care-of Addresses Registration”, draft-ietf-monami6-multiplecoa-01.txt, October 2006.